In recent years, a high capacity secondary battery, particularly a nonaqueous secondary battery utilizing the intercalation/deintercalation reaction of lithium ion, as an electric source for electronic apparatus such as portable telephone, video camera and note type personal computer has been in growing demand. Referring particularly to nonaqueous secondary batteries for the portable telephone, those having high capacity as well as good repeatability in use, i.e., good charge-discharge cycle characteristics have been desired.
In general, the secondary batteries are prepared by a process which comprises winding an element, inserting a wound element into a battery can, injecting an electrolyte into the can, sealing the can, and then ageing the element. These secondary batteries thus prepared are then examined for properties before shipping.
The ageing is normally effected for two weeks to a month, mostly at ordinary temperature. The ageing provides an effect of stabilizing the battery properties.
The inventors made extensive studies of ageing of secondary batteries. As a result, it was found that the charge-discharge capacity and cycle characteristics of the secondary batteries can be improved with ageing of the secondary batteries in which they are subjected to charging treatment having at least two two stages and storage treatment having at leat two times.